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Uniflow and Jett Engines

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Old 05-10-2009, 10:10 PM
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Broken Wings
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Default Uniflow and Jett Engines

Bob, I bought a Jett 120L and I want to install it on a OMP Fusion 67. The tank that came with the ARF is on the small side and I bought a Sullivan BT-16 which is a boat tank.

It's narrow, only about an 1 3/4" thickness by 3 3/4 x 5 3/4. It will fit the profile perfect and not hang out in the wind like a square tank.

I thought about using uniflow to eliminate the head pressure as the stopper is dead center.

Have you guys fooled around with Jett's and Uniflow tanks? The plane will probably be inverted as often as it is right side up. As well as every other vector.

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Old 05-11-2009, 08:18 AM
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Default RE: Uniflow and Jett Engines

Thanks for writing.....

I have not tried one myself, no. I know a few folks have played with them. Nothing really conclusive on how the performed differently than a standard fuel tank.

Uniflow (in my experience) works effectively on an engine that "sucks" or draws fuel. The venturi pressure drop that makes the fuel flow is small, so a change in tank head pressure can affect how that works very noticably. So on the CL applications (which often enough did not have a muffler or effective method of tank pressure) they were very useful.

You can not run the Jett engine without proper muffler pressure. The carb alone will not draw fuel well at full throttle (its a big carb). In general the Jett muffler pressure is substantial. It is a "push" fuel delivery. Overwhelems the fluid head pressure when the engine is running. Fuel delivery tends to remain pretty steady no matter what the tank level.... until you get below about 1/3 remaining fuel - when you have a higher risk of picking up an air bubble.

When the engine is off, yeah, you might get a bit of fuel drip. That may require a clamp/hemostat to keep the engine from flooding until you get it started.

The best solution for your application is to use a bubble-free setup. I understand the installation involved - difficult to make that work effectively. Your approach and reasoning is sound, and probably does look good too!

However I do know of one person who was running an OS120 on the Fusion with two Bubble-Jett 8oz tanks strapped to the side, and last I heard from him last summer it worked very well. Hi goal was flight duration, since the bubble tanks can run to "dry" without an air bubble risk. In actuallity he found that he was VERY rarely flying above 1/2 throttle and the fuel burn was a whole lot less than he antisipated. The Jett 120 is the same way. Yeah, it will burn 2oz a min at full song..... throttle back and that drops quite a bit.

I hope this helps.....

Bob
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Old 05-11-2009, 06:37 PM
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Default RE: Uniflow and Jett Engines

I'll try it the way it is and see how she runs. I like this engine....
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